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Old 05-25-2020, 08:42 AM   #3823
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Suspension tuning

So I was reading a bit about suspension tuning. Which make my head hurt since theres a lot of conflicting info on the subject.
It had me thinking about the differences in autocross vs track use when I came across this statement.
"Generally, you want more compression and less rebound on a road course, but less compression and more rebound for autocross."
First I thought, is that accurate? Also, can it really be that simple as a baseline?

So lets say I have RCE Tarmac2's (separate adjustable compression and rebound) with the provided 400lbs springs and RCE front and rear sway bars on soft. As an experiment, I use the vendors recommended compression and rebound settings as a middle of the road baseline. Then create an autocross baseline by going a couple click in the direction suggested by the earlier statement and do the same for a track baseline. Not making any other changes, drive the car in both scenarios and adjust each baseline as needed.
Curious as to what you think?
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Old 05-26-2020, 11:13 AM   #3824
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Originally Posted by bmacfrs View Post
So I was reading a bit about suspension tuning. Which make my head hurt since theres a lot of conflicting info on the subject.
It had me thinking about the differences in autocross vs track use when I came across this statement.
"Generally, you want more compression and less rebound on a road course, but less compression and more rebound for autocross."
First I thought, is that accurate? Also, can it really be that simple as a baseline?

So lets say I have RCE Tarmac2's (separate adjustable compression and rebound) with the provided 400lbs springs and RCE front and rear sway bars on soft. As an experiment, I use the vendors recommended compression and rebound settings as a middle of the road baseline. Then create an autocross baseline by going a couple click in the direction suggested by the earlier statement and do the same for a track baseline. Not making any other changes, drive the car in both scenarios and adjust each baseline as needed.
Curious as to what you think?
That's a BIG simplification....but not a terrible one. At least for rebound, yes I generally prefer more on an autox car compared to a track car. But still not "too much" rebound which we often see on track/autox/street. For compression...maybe more compression for a track car but it's very dependent on other factors.

Generally, people just run too much rebound and not enough compression for both autox and the track and the street. Very broad statement but it's a thing IMO.

It's common to prefer different settings for track vs autox for T2s. That's the beauty of a 2 way damper as long as you take notes and make the right adjustments. I think your experiment is worthwhile, but just remember to take notes and don't assume anything will be better because the internet says it should be!

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Old 05-31-2020, 04:49 PM   #3825
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@Racecomp Engineering or @CSG Mike, I have a hypothetical suspension question.

Imagine you have a set of shocks and springs well matched for each other, like RCE Yellows with the stock shocks they were designed to work with. if you added significantly stiffer sway bars to that setup, would you need to go back and get stiffer shocks to keep the car from being underdamped in roll?

Thanks!
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Old 05-31-2020, 06:44 PM   #3826
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Originally Posted by Yoshoobaroo View Post
@Racecomp Engineering or @CSG Mike, I have a hypothetical suspension question.

Imagine you have a set of shocks and springs well matched for each other, like RCE Yellows with the stock shocks they were designed to work with. if you added significantly stiffer sway bars to that setup, would you need to go back and get stiffer shocks to keep the car from being underdamped in roll?

Thanks!
Depends on what you do with the car, but possibly.
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Old 05-31-2020, 09:45 PM   #3827
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CSG and RCE tag-team suspension Q&A thread! Ask us anything!



Mostly daily driving, 3-5 AutoX a year, one HDPE a year.

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Old 06-01-2020, 10:03 AM   #3828
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Originally Posted by Yoshoobaroo View Post
@Racecomp Engineering or @CSG Mike, I have a hypothetical suspension question.

Imagine you have a set of shocks and springs well matched for each other, like RCE Yellows with the stock shocks they were designed to work with. if you added significantly stiffer sway bars to that setup, would you need to go back and get stiffer shocks to keep the car from being underdamped in roll?

Thanks!
Short answer...yes, the swaybar stiffness should be taken into account with your dampers.

Longer answer...if you only have 4 dampers like most of us, this means you're making a compromise. The "ideal" 65% critically damped number that's thrown around is usually only in reference to your main springs and dampers. So that's fine for ride but for roll you also have the swaybars working. It's possible to have more than 4 dampers so you can isolate all the different body motions but that's not really a thing for normal cars.

In practice...if you have adjustable shocks this is one area they can help. But shocks that are poorly matched to the main springs is MUCH more noticeable than when they don't really match the main springs + roll bars. In some cases, the benefit of the extra roll resistance may outweigh the drawbacks but it depends on other factors. So you may not need to worry about it too much in practice.

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Old 06-01-2020, 03:20 PM   #3829
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Originally Posted by Yoshoobaroo View Post
Imagine you have a set of shocks and springs well matched for each other, like RCE Yellows with the stock shocks they were designed to work with. if you added significantly stiffer sway bars to that setup, would you need to go back and get stiffer shocks to keep the car from being underdamped in roll?
Not exactly answering your question, but sharing just in case it's helpful:

Last few weeks I've been practicing AutoX in a simulator (Live for Speed) with friends, and among other things we've been working on car setups. At first we were using the standard approach: "do a few runs, determine what the problem probably is, then change some parameters as fancy books say". After many iterations, we ended up with setups that were reasonably fast, but I really didn't like how the cars handled. They were hard to drive, the balance was all over the place throughout corners, trail braking was hit-or-miss, and overall it wasn't pleasant to drive them.

Then I dug up some old posts on LFS forum and decided to try a "setup analyzer" app (VHPA). The app does some magic math and gives you info on understeer/oversteer balance info throughout 5 different stages of a corner, as well as a lot of other info. In just 15 minutes I was able to create a new setup with completely reworked suspension parameters, that was so much easier to drive, and after a couple of minor iterations, I started setting new PBs!

It's mind-blowing how much time and money can one waste by trying things "by the book" in real life if they're not already super experienced, let alone when they follow contradicting inputs of unknown credibility (internet, local mechanics, "experienced" friends, etc.).

Having that said, I encourage everyone who wants to significantly re-work their suspension to first practice in a sim to build a good sense of how setups work and how to get good feedback after setup changes — before spending any significant money on changes to their real car.
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Old 06-01-2020, 03:30 PM   #3830
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One of the problems with making set up changes based "on the book" or the internets is that it's usually really hard to change 1 thing without affecting another thing.

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Old 06-01-2020, 05:55 PM   #3831
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CSG and RCE tag-team suspension Q&A thread! Ask us anything!

I'm still a noob, learning and reading. Does the shock dyno graph gives information on what spring rates can be paired for the said dampers? (taking into consideration what I'm trying to achieve from the dampers)

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Old 06-01-2020, 08:37 PM   #3832
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Then I dug up some old posts on LFS forum and decided to try a "setup analyzer" app (VHPA). The app does some magic math and gives you info on understeer/oversteer balance info throughout 5 different stages of a corner, as well as a lot of other info. In just 15 minutes I was able to create a new setup with completely reworked suspension parameters, that was so much easier to drive, and after a couple of minor iterations, I started setting new PBs!
This sound magical.
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Old 06-02-2020, 09:22 AM   #3833
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I'm still a noob, learning and reading. Does the shock dyno graph gives information on what spring rates can be paired for the said dampers? (taking into consideration what I'm trying to achieve from the dampers)
Yes, with some math. I will do an article on that eventually and post it first on our @theapexfiles instagram page. Eventually I'm going to repost all of those here.

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Old 06-02-2020, 12:23 PM   #3834
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Yes, with some math. I will do an article on that eventually and post it first on our @theapexfiles instagram page. Eventually I'm going to repost all of those here.

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Looking forward to that.
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Old 06-10-2020, 05:47 AM   #3835
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I need to ADD some weight to my car (around 88lbs) in order to qualify for a certain class in a local competition.

There are 2 points that I can use to safely attach the weights (tested both):
- in the trunk, using some spare wheel (~40lbs) or gym weights (up to 88lbs)
- between passenger seat and the back seat (by replacing the screw that holds the back seat with a longer one) using gym weights (up to 88lbs)

My ride (details relevant to my question):
- stock suspension (with camber bolts and camber adjustable bushings in the front, rear LCA) for some -1.5/-1.0 camber f/r
- sport cup2 tires, 225/40/18 on Alleggerita wheels (~38lbs per wheel)
- NA with OFT stage2+ (Tomei UEL headers, Q300 CB)
- Stoptech/XP10 rotors/pads
- proper track orientated oils/liquids
- stock everything else

My question is, where should I put the weights with minimal impact to the car's balance? Are there any other anchor points that I can use (as lower as possible)?
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Old 06-10-2020, 06:15 AM   #3836
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I'd probably use 2nd option, between seats, and closer to tranny tunnel, to reduce rotational moment of inertia. You can also consider corner weighting with you sitting in car, and decide if weights are better to be put after driver or after passenger seat on other side, to even out weights per wheel. 1st option in trunk behind rear axle imho might be preferred only if you want to shift car weight distribution to rear and ease access/changing weights .. possibly if for ice racing, not so much for summer tarmac track.
If it's about track performance/handling, i'd probably think of more front camber. Front LCA camber-adjustable bushing by Powerflex + camberbolts in both holes should enable to reach upto -3. Another option is to use offset rubber topmount by Pedders. If you need only -3, then you can replace that camber LCA bushing or one of camberbolts with that topmount to net similar total camber. Rear LCA .. IIRC there was limit how much camber could be dialed in with Whiteline camber bushings and adjusting was PITA, i'd rather think of normal adjustable rear LCA. I'd aim for -2 to -2.5 rear camber (with front -3). If you are serious about dialing optimum alignment, consider purchase of pyrometer.
Cup2 have loads of grip .. hmm, i wonder if stock suspension/springs aren't too soft for them? Imho you often might be on bumpstops.
Obviously, decisions on many choices on suspension mods should come from what is allowed or not and how heavy penalized in your mentioned certain class.
You can also consider installing brake airducts to increase stock brakes capabilities.
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